The invention relates to an electrical shutter of electromagnetic release type for camera, and more particularly to such shutter in which one revolution of shutter drive member is effective to open and close the shutter blades.
An electrical shutter of electromagnetic release type is known which includes a prime mover spring disposed on a single shaft and which is charged in response to a film winding operation. It is effective, in response to an electromagnetic release, to drive a shutter drive member for rotation in order to operate the shutter blades. When the shutter is open, the rotation of the shutter drive member is controlled by a detent member which is constrained by an electromagnet, thereby achieving a desired exposure period. Such an electrical shutter is simple in construction and permits an automatic stop of a film winding operation for each picture frame. In addition, it prevents a double exposure by virtue of its inherent mechanism.
FIG. 1 shows a conventional arrangement of shutter mechanism of such single shaft rotating type. In this Figure, shutter drive member 101 is in the form of disc and is fixedly mounted on a single rotatable shaft 102, on which prime mover spring 103 is disposed having its one end 103a secured to drive member 101 and its other end 103b fixedly connected with charging member 109 which is adapted to rotate in response to a film winding operation. Thus spring 103 is charged through a film winding operation. The spring urges drive member 101 to rotate counter-clockwise, as indicated by an arrow. However, the resulting rotation of drive member 101 is blocked by the abutment of an arm 101a extending therefrom against bevelled edge 105a on locating member 105 which is pivotally mounted on pin 104, whereby drive member 101 is maintained at its start position to initiate a shutter operation.
Bevelled edge 105a is formed on the end of one arm of locating member 105, which includes another arm 105b which is adapted to be held attracted to release electromagnet Mg1. Normally, locating member 105 is urged to rotate clockwise about pin 104 by spring 110, whereby arm 105b is urged against electromagnet Mg1 while bevelled edge 105a bears against arm 101a to maintain shutter drive member 101 at its start position.
Detent member 106 has one arm 106a which is located on the path of rotation of arm 101a. Detent member 106 is pivotally mounted on pin 107 and is urged by spring 108 to rotate counter-clockwise about pin 107, whereby the end of the other arm of detent member 106 abuts against another electromagnet Mg2.
With the shutter mechanism described above, the depression of release button (not shown) activates an electrical shutter circuit to demagnetize electromagnet Mg1, whereupon locating member 105 is released from constraint thereof, allowing bevelled edge 105a to be raised by the arm 101a as the latter rotates counter-clockwise under the resilience of prime mover spring 103 in order to open shutter blades. In the fully open position of the shutter, arm 101a bears against arm 106a of detent member 106 to maintain the shutter fully open for a given period of time. At this time, electromagnet Mg2 holds detent member 106 attracted thereto. When a proper exposure has been achieved, electromagnet Mg2 is deenergized, whereupon drive member 101 rocks detent member 106 against the resilience of spring 108 to continue its rotation about shaft 102 through the remaining half-revolution to return to its start position, thus closing the shutter blades.
In the conventional arrangement of the single shaft rotating type described above, shutter drive member 101 is maintained at its start position by the abutment of its arm 101a against bevelled edge 105a on locating member 105. The purpose of this design is to prevent a starting lag in the shutter of electromagnetic release type, by allowing a rotation of drive member 101 to open shutter blades to occur immediately when electromagnet Mg1 is deenergized as a result of providing an abutting engagement between arm 101a and bevelled edge 105a. However, it will be appreciated that as spring 103 is charged in response to a film winding operation, the resilience stored therein which urges arm 101a against bevelled edge 105a progressively increases. This means that the retention of drive member 101 at its start position by means of locating member 105 may be unstable during the charging operation.
On the other hand, when a strobo unit and/or data entry unit is mounted on a camera incorporating an electrical shutter, a signal which actuates the unit is derived from an X contact switch provided on the part of camera. Referring to FIG. 2, an illumination initiate signal to strobo unit 50 or an entry initiate signal to data entry unit 51 is provided by X contact switch SW30 which is closed in the fully open position of the shutter. Strobo unit 50 includes a power source 52 across which main capacitor 53 and flash discharge tube 54 as well as a series circuit including resistor 55 and illumination test switch SW4 are connected in parallel. The switch SW4 is shunted by a series circuit including trigger capacitor 56 and trigger transformer 57. The X contact switch SW30 is connected in parallel with switch SW4. Consequently, when X contact switch SW30 is closed, the trigger circuit is driven to provide a strobo illumination in synchronized relationship with the fully open condition of the shutter, thereby permitting a flash photography. When it is desired to test strobo unit 50, a test button (not shown) is depressed to close switch SW4 to see if the strobo unit 50 operating properly. It will also be noted that data entry unit 51 is also connected with switch SW30, the closure of which achieves a data entry.
However, when switch SW30 is connected in common with strobo and data entry units 50, 51 as shown, the closure of test switch SW4 not only initiates an illumination by strobo unit 50, but also achieves a data entry by unit 51. Therefore, if a picture is taken under flashlight illumination subsequent to such illumination test, data entry unit 51 will be operated for the second time to provide a double data entry, causing a blurring of data and an overexposure.